Thermally variable resistance



March 1, 1966 c. s. MERTLER 3,238,486

THERMALLY VARIABLE RESISTANCE Original Filed March 2. 1960 2Sheets-Sheet 1 Fly. INVENTOR.

CHARLES S. MERTLER w flz' MM ATTOR EYS March 1, 1966 5, E L 3,238,486

THERMALLY VARIABLE RESISTANCE Original Filed March 2. 1960 2Sheets-Sheet 2 I52 as /s| INVENTOR.

CHARLES 8. ME RTLER ATTO NEYS United States Patent 3,238,486 THERMALLYVARIABLE RESISTANCE Charles S. Mertler, Mansfield, Ohio, assignor toStevens Manufacturing Company, Inc., a corporation of Ohio Originalapplication Mar. 2, 1960, Ser. No. 12,408, now

Patent No. 3,107,288, dated Oct. 10, 1963. Divided and this applicationJan. 7, 1963, Ser. No. 249,788

Claims. (Cl. 338-25) This application is a division of my applicationSerial Number 12,408, filed March 2, 1960, now Patent No. 3,107,288entitled Temperature Sensing Unit.

The invention relates in general to a temperature sensing unit and moreparticularly to the electrical and physical arrangement of a temperaturesensing unit which may be used with an electrical heating device. Inhousehold ranges, surface units are employed to heat vessels, and inrecent years surface units have come into use wherein the heat output iscontrolled according to the temperature of the vessel. This permitsvarious degress of heat for different cooking needs and most importantlyprevents overcooking or burning, for example, if the liquid in thevessel should boil away. In such automatic surface controlled units thetemperature of the vessel being heated should be accurately determined.Accordingly, temperature sensing units have been employed generally atthe center of the surface unit, but in the past many of these have beenunsatisfactory in that they have failed to accurately determine thetemperature of the vessel or have had a considerable time lag in sensingthe temperature.

Accordingly, an object of the invention is to provide a thermallyvariable resistance as a temperature control for a surface heating unitwherein a resistance wire is wrapped as a double spiral wire in a singleaxial thickness between metal members for good heat transfer thereto andto utilize all of a predetermined length of the resistance wire.

Another object of the invention is to provide a temperature sensing unitfor a surface unit which will accurately determine the temperature of avessel heated on the surface unit and with no appreciable time lag.

Still another object of the invention is to provide a rugged and simpletemperature sensing unit, which is consistent in operation, and oneusing solid non-telescoping connections inside the unit to preventbreakage of wires.

Still another object of the invention is to provide a temperaturesensing unit for a surface unit which is small and effectively heatinsulated from the temperature of the surface unit itself and yetrapidly responsive to change of temperature of the vessel by having asmall heat mass.

Still another object of the invention is to provide a temperaturesensing unit for a range surface unit wherein the sensing unit may beused with many different manufactured types of surface units and notinterfere with the operation or cleaning of any such surface unit andalso to provide a ready means of mounting the sensing unit which iscompatible with all surface units.

Other objects and a fuller understanding of the invention may be had byreferring to the following description and claims, taken in conjunctionwith the accompanying drawings, in which:

FIGURE 1 is a partial top view of a range surface unit with which thetemperature sensing unit of the invention may be used;

FIGURE 2 is a sectional view on line 2-2 of FIG- URE 1;

FIGURE 3 is an enlarged sectional view on line 3-3 of FIGURE 2; and

FIGURE 4 is a sectional view on line 4-4 of FIG- URE 3.

The invention is shown in FIGURES 1 and 2 as a tem- Patented Mar. 1,1966 Ice perature sensing unit indicated generally at 11 which may beused with a surface heating unit 12 shown as an electrical heating unit,and mounted on the frame 13 or top of some form of range, such as ahousehold electric range. The surface heating unit 12 may be of anydesired construction and is shown as being of generally spiralconfiguration having first and second ends 14 and 15 which aremechanically connected to a terminal block 16 carried on the frame 13.This terminal block 16 may provide a flexible electrical permanentconnection to the surface heating unit 12 or may provide adisconnectable electrical connection for the heating unit 12. There aretwo such general types of heating units 12 currently on the market andin one the heating unit 12 may be completely removed from the range forcleaning and in others this heating unit 12 may merely be swung out ofthe way through an arc so that a drip pan 17 underneath the heatingunits 12 may be cleaned. The present invention of a temperature sensingunit 11 may be used with either type. The drip pan 17 is supported insome manner from the frame 13 below the surface heating unit 12 andincludes a central aperture 18.

The temperature sensing unit 11 includes a flat thin plate support 21which has an L-shaped bottom extension 22. The plate support 21 is thinenough to be mounted at the terminal block 16 by the same screws 23which mount this terminal block 16. This provides for a convenientmounting of the entire sensing unit 11 by the same means which supportthe heating unit 12 at the terminal block A relatively rigid bracket 26has first, second'and third leg portions 27, 28 and 29, respectively,and the end of the first leg portion 27 is fixedly attached to the L-shaped extension 22 by any suitable means, such as the rivets 30. Thefirst leg portion 27 extends generally horizontally under the drip pan17 and the second leg portion 28 extends generally vertically upwardlythrough the drip =pan aperture 18. This places the third leg portion 29at a level above the drip pan 17 and it extends generally horizontallyunderneath the center or axis 31 of the heating unit 12.

The third leg portion 29 has a surface defining an aperture 34 on thisaxis 31. An insulator sensor body 35 has a flanged head 36 and alongitudinally extending shank 37. This shank 37 is cylindrical and isslidably received in the third leg portion 29. A coil compression spring38 surrounds the shank 37 and engages the head 36 and the third legportion 29 to urge upwardly the sensor body 35. A snap ring 39 engages agroove 40 in the lower end of the shank 37 so as to retain the body 35within the bracket 26. A coaxial recess 43 is provided in the upper endof the head 36 and the shank 37 is longitudinally apertured at 44. Ametal cap 45 of good heat conductivity is provided at the upper end ofthe head 36 and a stem 46 is attached to the cap 45. A metal backupmember or washer 47 is received on the stem 46 and defines with theunderside of the cap 45 an annular wire space 48. Both the cap 45 andthe backup washer 47 may be made of aluminum, for example. The metalbackup washer 47 has first and second apertures 49 and 50 closelyadjacent the stem 46. First and second wire ends 51 and 52 of aresistance wire 53 pass through these apertures 49 and 50 and thisresistance wire 53 is wrapped on the stem 46 as a doubled wire in apancake coil in a single axial thickness in the annular wire space 48.This configuration is best shown in FIGURE 4. This wrapping as a doublespiral assures that the two wire ends 51 and 52 may be at the innerperiphery of the coiled resistance wire 53 without any crossovers of thewire and also assures that all of the wire 53 of a predetermined lengthis completely used in the coil in the wire space 48 without having tocut off any of the length of the wire 53 which otherwise might not havegone one more turn around the outer periphery of this coil of wire, ifone terminal were at the outer periphery. This assures accuracy inlength of the wire 53, and hence, accuracy of the predeterminedresistance thereof.

An insulating washer 56 abuts the metal backup washer 47 and it also hasapertures 57 for the wire ends 51 and 52 to pass through, An insulatingeyelet support washer 58 carries first and second eyelets 59 and 6t) andthe heads of these eyelets are disposed between the insulating washer 56and the eyelet support washer 58 for mutual insulation as well assupport of these eyelets. First and second terminal pins 61 and 62 arelongitudinally disposed in the body and pass through the longitudinalaperture 44. These terminal pins 61 and 62 are solid and non-telescopingand are received in the eyelets 59 and 60, respectively, andfrictionally grip the wire ends 51 and 52 by being wedged into theeyelets. The terminal pins extend to the lower end of the body shank 37and are headed at 63 to receive blade type terminals 64 and 65. Theseterminals 64 and 65 thus provide external electrical connections to theresistance wire 53 through flexible leads 66.

The insulator sensor body 35 has a relatively small physical size andbeing made of good heat insulation receives a minimum of heat from thesurface heating unit 12. The normal position of the sensor body 35places the metal cap above the level of the heating unit 12, and thus,when any vessel is placed on the heating unit this compresses the spring38. The urging of this spring 38 maintains the cap 45 in engagement withthe vessel for good heat transmissibility to the cap 45. The resistancewire 53 may be insulated with glass insulation which provides excellentelectrical insulation with a minimum of thickness, yet the homogeneityprovides relatively good heat conductivity to the wire itself. Actually,only a low voltage need be applied to the resistance wire 53, andaccordingly, only low voltage insulation is required. Also, the goodheat conductivity of the metal cap 45 and the metal backup washer 47,since they are made of aluminum, and the single layer of resistance wirein intimate contact therebetween, contribute to the rapid heat responseof the resistance wire 53. This means that the resistance of this wire53 readily follows the change in temperature of the vessel being heatedby the surface unit 12. Accordingly, the resistance of the resistancewire changes quite appreciably, in the order of 2 /2 to 1 over thetemperature range from room temperature to high cooking temperatures.

The entire temperature sensing unit 11 is rugged, simple and dependable,since no flexible wires are utilized inside the sensor body 35 whichmight break upon repeated flexing.

Although this invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

1. A thermally variable resistance element comprising, in combination, ametal plate,

a metal back up member,

means to carry said metal back up member spaced from said metal plate todefine an annular wire space therewith,

an insulated resistance wire having first and second ends with both saidends disposed near the center of said back up member,

and said resistance wire being spiral wrapped as a doubled wire in asingle axial thickness in said annular wire space and with a closedintegral end at the outer periphery.

2. A thermally variable resistance element comprising,

in combination, a metal plate,

central stem means fixed to one face of said plate,

a metal washer carried on said stern means and spaced from said plate todefine an annular wire space therewith,

an insulated resistance wire having first and second ends,

said resistance wire being spiral wrapped as a doubled wire in a singleaxial thickness in said annular wire space and with aclosed integralend,

and successive turns lying substantially in engagement with adjacentturns to utilize the complete length of a predetermined length of saidresistance wire regardless of the peripheral position of the closed endof said coil relative to said wire ends.

3. A thermally variable resistance element comprising, in combination, ametal plate,

a metal back up member,

means to carry said metal back up member spaced from said metal plate todefine an annular wire space therewith,

an insulated resistance wire having first and second ends with both saidends disposed near the center of said back up member,

said resistance wire being spiral wrapped as a doubled wire in a singleaxial thickness in said annular wire space and with a closed integralend at the outer periphery,

and the first turn of said coil being wrapped near the center of saidback up member and successive turns lying substantially in engagementwith adjacent turns to utilize the complete length of a predeterminedlength of said resistance wire regardless of the peripheral position ofthe closed end of said coil relative to said wire ends.

4. A temperature sensing element comprising, in combination, a metalplate of good heat conductivity,

a central stem fixed to one face of said plate and substantially normalthereto,

a metal washer of good heat conductivity carried on said stem and spacedfrom said plate and substantially parallel thereto to define an annularwire space therewith,

a resistance wire having first and second ends with both said endsdisposed close to said stem,

said resistance wire being spiral wrapped as a doubled wire in a pancakecoil in a single axial thickness in said annular wire space and with aturned back on itself closed integral end at the outer periphery,

and first and second terminals mounted fixed relative to said plate anddisposed closely adjacent said stem and said washer and connected tosaid first and second wire ends, respectively.

5. A thermally variable resistance element comprising, in combination, ametal plate,

central stem means fixed to one face of said plate,

a metal washer carried on said stern means and spaced from said plate todefine an annular wire space therewith,

an insulated resistance wire having first and second ends with both saidends disposed close to said stern means,

said resistance wire being spiral wrapped as a doubled wire in a singleaxial thickness in said annular wire space and with a closed integralend at the outer periphery,

and the first turn of said coil being wrapped around said stem means andsuccessive turns lying substantially in engagement with adjacent turnsto utilize the complete length of a predetermined length of saidresistance wire regardless of the peripheral position of the closed endof said coil relative to said wire ends.

6. A thermally variable resistance element comprising,

in combination, a metal plate,

central stem means fixed to one face of said plate,

a metal washer carried on said stem means and spaced from said plate todefine an annular wire space therewith,

an insulated resistance wire having first and second ends with both saidends disposed close to said stem means,

said resistance wire being spiral wrapped as a doubled wire in a singleaxial thickness in said annular wire space and with a closed integralend at the outer periphery,

an apertured insulating plate disposed over said central stem means,

wire apertures in said insulating plate with said wire ends passingtherethrough,

a terminal washer having an aperture and disposed on said central sternmeans,

metal terminals insulatedly carried in said terminal washer,

and means connecting said wire ends to said terminals in said terminalwasher.

7. A temperature sensing element comprising, in combination, a metalplate of good heat conductivity,

a central stem fixed to one face of said plate and substantially normalthereto,

a metal washer of good heat conductivity carried on said stem and spacedfrom said plate and substantially parallel thereto to define an annularwire space therewith an insulated resistance wire having first andsecond ends with both said ends disposed close to said stem,

said resistance wire being spiral wrapped as a doubled wire in a singleaxial thickness in said annular wire space and with a closed integralend at the outer periphery,

the first turn of said coil being wrapped around said stem andsuccessive turns lying substantially in engagement with adjacent turnsto utilize the complete length of a predetermined length of saidresistance wire regardless of the peripheral position of the closed endof said coil relative to said wire ends,

an insulating plate having aperture means to be received on said centralstem and to pass said wire ends therethrough,

metal terminals insulatedly carried relative to said stem,

and means connecting said wire ends to said terminals.

8. A temperature sensing element comprising, in combination, a metalplate of good heat conductivity,

at central stem fixed to one face of said plate and substantially normalthereto,

a metal washer of good heat conductivity carried on said stern andspaced from said plate and substantially parallel thereto to define anannular wire space therewith,

an insulated resistance Wire having first and second ends with both saidends disposed close to said stem,

said resistance wire being spiral wrapped as a doubled wire in a singleaxial thickness in said annular wire space and with a closed integralend at the outer periphery,

the first turn of said coil being wrapped around said stem andsuccessive turns lying substantially in engagement with adjacent turnsto utilize the complete length of a predetermined length of saidresistance wire regardless of the peripheral position of the closed endof said coil relative to said wire ends,

a terminal washer having an aperture and disposed on said central stem,

metal terminals insulatedly carried in said terminal washer,

and means connecting said wire ends to said terminals in said terminalwasher.

9. A temperature sensing element comprising, in com- 10 bination, ametal plate of good heat conductivity,

a central stem integrally fixed to one face of said plate andsubstantially normal thereto,

a metal washer of good heat conductivity carried on said stern andspaced from said plate and substantially parallel thereto to define anannular wire space therewith,

an insulated resistance wire having first and second ends with both saidends disposed close to said stem,

said resistance Wire being spiral wrapped as a doubled wire in a pancakecoil in a single axial thickness in said annular wire space and with aturned back on itself closed integral end at the outer periphery,

the first turn of said coil being Wrapped around said stem andsuccessive turns lying substantially in engagement with adjacent turnsto utilize the complete length of a predetermined length of saidresistance wire regardless of the peripheral position of the closed endof said coil relative to said wire ends,

an apertured insulating plate disposed over said central stem,

wire aperture means in said insulating plate with said wire ends passingtherethrough,

a terminal washer having an aperture and disposed on said central stem,

metal terminals insulatedly carried in said terminal washer,

and means connecting said wire ends to said terminals in said terminalwasher.

10. A temperature sensing element comprising, in combination, a metalplate of good heat conductivity, a central stem fixed to one face ofsaid plate and substantially normal thereto, a metal washer of good heatconductivity carried on said stem and spaced from said plate and substantially parallel thereto to define an annular wire space therewithwith an inner periphery adjacent said stem and with an outer periphery,an insulated resistance wire having first and second ends with both saidends disposed at one periphery, said resistance wire being spiralwrapped as a doubled wire in a single axial thickness in said annularwire space and with a closed integral end at the other periphery, thefirst turn of said coil being Wrapped adjacent said stem and successiveturns lying substantially in engagement with adjacent turns to utilizethe complete length of a predetermined length of said resistance wireregardless of the peripheral position of the closed end of said coilrelative to said wire ends, metal terminals insulatedly carried relativeto said stem, and means connecting said wire ends to said terminals.

References Cited by the Examiner UNITED STATES PATENTS 2,703,833 3/1955Vanvor 338--28 2,980,875 4/1961 Sivacek 33825 3,042,783 7/1962 Mertler219 -20.41

RICHARD M. WOOD, Primary Examiner,

10. A TEMPERTURE SENSING ELEMENT COMPRISING, IN COMBINATION, A METALPLATE OF GOOD HEAT CONDUCTIVITY, A CENTRAL STEM FIXED TO ONE FACE OFSAID PLATE AND SUBSTANTIALLY NORMAL THERETO, A METAL WASHER OF GOOD HEATCONDUCTIVITY CARRIED ON SAID STEM AND SPACED FROM SAID PLATE AND SUBSTANTIALLY PARALLEL THERETO TO DEFINE AN ANNULAR WIRE SPACE THEREWITHWITH AN INNER PERIPHERY ADJACENT SAID STEM AND WITH AN OUTER PERIPHERY,AN INSULATED RESISTANCE WIRE HAVING FIRST AND SECOND END WITH BOTH SAIDENDS DISPOSED AT ONE PERIPHERY, SAID RESISTANCE WIRE BEING SPIRALWRAPPED AS A DOUBLED WIRE IN A SINGLE AXIAL THICKNESS IN SAID ANNULARWIRE SPACED AND WITH A CLOSED INTEGRAL END AT THE OTHER PERIPHERY, THEFIRST TURN OF SAID COIL BEING WRAPPED ADJACENT SAID STEM AND SUCCESSIVETURNS LYING SUBSTANTIALLY IN ENGAGEMENT WITH ADJACENT TURNS TO UTILIZETHE COMPLETE LENGTH OF A PREDETERMINED LENGTH OF SAID RESISTANCE WIREREGARDLESS OF THE PERIPHERAL POSITION OF THE CLOSED END OF SAID COILRELATIVE TO SAID WIRE ENDS, METAL TERMINALS INSULATEDLY CARRIED RELATIVETO SAID STEM, AND MEANS CONNECTING SAID WIRE ENDS TO SAID TERMINALS.